Read if you like; I’m not a physicist so this isn’t going to sound very technical or mathematical or anything, it’s just an idea I came up with. It’s based off my limited understanding of entropy, gravity, and the Poincare Recurrence Theorem.
You’ve stumbled onto a line of thinking with a long history. I wish to make a couple comments before talking about some current models of this phenomenon (cyclic universe).
(1). The temperature of the universe will decrease, but it will never actually reach absolute zero. It will do so only in the infinite future.
(2). Not all matter will gather together. For instance, there is plenty of gas floating around which will never come into contact with a very massive body. So in the far future, we will have light and atoms floating around, getting more and more spread out as the universe expands (even taking into account the acceleration of the expansion).
Onto the modern incarnations of the cyclic universe which essentially takes the Poincare recurrence theorem seriously. Mind you, Poincare recurrence requires the system in question be a closed system (we’d think the universe doesn’t “leak” anything out of the universe so that’s fine) as well as some other subtle points which probably do hold for the universe as a whole.
The current thinking (controversial — there is nothing to really indicate this is true) is that maybe (maybe) the Big Bang was created merely as some quantum fluctuation of the vacuum. The vacuum just up and decided (randomly, of course) to give us something from nothing. So then, in the far future where we have as much time as we want, perhaps the vacuum (space will be very close to vacuum: no light, no matter, just empty spacetime) and this can happen again.
So this cyclic behavior doesn’t require a black hold or a collection of matter. But maybe it is helped along with these things.